The long range purpose of this research is to develop a non invasive method using MRS for the characterization of estrogen responsiveness of breast carcinoma. To that end, specific metabolic activities modulated by estrogens and by antiestrogens will be characterized in human breast cancer cell lines that retain the receptors for steroid hormones: MCF-7, T47D and ZR-75-1. This research is part of our general efforts to characterize hormonal induced changes in the reproductive organs and associated malignancies (see Appendix). The search will concentrate on activities that are known to be enhanced by estrogen in genuine target organs such as: 1) the activity of creatine kinase (the BB isozyme), a favored early marker of estrogen action; 2) several key enzymes of the glycolytic pathway; and 3) glucose-6-phosphate dehydrogenase (G6PD), for which increased production of mRNA has been observed. In addition, it is anticipated that the ability to monitor the metabolism on line, in active growing cells, will lead to the discovery of unpredicted changes as seem to occur with the concentration of the glycerol derivatives of phosphorylcholine and phosphorylethanolamine. NMR spectroscopy will be the main tool in this study. Methods for keeping the cells alive, active and growing during the NMR measurements were developed. 31-P NMR will be employed for determining the energetics of the cells and the kinetics of phosphate transfer reactions. 13-C NMR studies will mainly concentrate on real time follow up of labeled substrates, intermediates, and end products providing a measure of the fluxes through the glycolytic enzymes and G6PD. 1-H NMR measurements and 1-H observed 13-C decoupled sequences will complement the 13-C results. The methodologies and the results of this research will subsequently be used in MRS studies of these human breast cancer cell lines, implanted in nude mice, and of breast tumors in humans.